The present invention relates generally to fuel cells, and more particularly, to fuel cells that consume gaseous hydrogen-containing fuels and produce electrical energy and water.
Typically, such a fuel cell generates water in the normal course of power generation using oxygen in the air to electrochemically combine with hydrogen gas to produce electrical energy by well-known electrochemical principles. Advantageous fuel cells for energy conversion are described in my U.S. Pat. Nos. 4,863,813; Re34,248; 4,988,582 and 5,094,928. In a fuel cell of the type described therein, a hydrogen-containing material at room temperature, such as a gaseous mixture of hydrogen and oxygen, is directly converted to direct-current electrical energy and the only reaction product is water.
In one such specific illustrative fuel cell, a submicrometer-thick gas permeable ionically conducting electrolytic membrane made of pseudoboehmite is deposited on an electrode that comprises a platinized impermeable substrate. A layer of platinum, for example, is deposited on the top surface of the membrane to form the other electrode of the fuel cell, which electrode is porous enough to allow the gas mixture to pass into the membrane. In a hydrogen/air mixture, such a fuel cell provides useful current at an output voltage as large as about one volt. While the voltage and current provided by the basic fuel cell are adequate for many applications of practical interest, I recognized that it would be desirable to devise a compact source of hydrogen for this and other fuel cells especially for portable electronic device applications, such as laptop computers and mobile phones. A suitable combination of a fuel cell with a lightweight, low volume source of hydrogen, could provide an improved source of power for portable electronic applications compared with batteries.
Several chemical hydride materials, with a high hydrogen content, react with water to yield hydrogen. The combined weight and volume of a chemical hydride and the water necessary to react with it to make hydrogen for use in a fuel cell, is termed the “specific energy” content of the fuel, which is normally measured in terms of Watt-hours (energy content) divided by the weight or volume of the chemical hydride plus its needed reactant water. Hence Watt-hours per kilogram or Watt-hours per liter are examples of the specific energy of a fuel for a fuel cell. In a portable application, a fuel cell with its fuel, termed a fuel cell system, would benefit from the use of a high specific energy fuel which would thereby reduce the carrying weight and volume of the fuel cell system.
I recognized that since a fuel cell produces water as a by-product during the normal course of its power-generating operation, a fuel cell that can use this by-product water as the reactant with a chemical hydride fuel would be advantageous in raising the specific energy of a fuel cell system by eliminating the need to carry additional water. Only one reactant, the chemical hydride, would then need to be carried in the fuel cell system. I recognized that fuel cells that could tolerate air mixed with their fuel supply would particularly benefit from such a method of generating hydrogen. I also recognized that a chemical means of control of the rate of hydrogen generation in such a fuel cell system would be advantageous. I further recognized that a portable fuel cell system would benefit from a means to collect the water produced during normal production of electrical energy to avoid wetness and flooding in the vicinity of the operating fuel cell.